The invention relates to an elevator bail for use in drilling operations, well testing and well maintenance operations. Particularly the invention relates to an elevator bail for use on a vessel conducting such operations above a riser from a seabed.
It is well known within the art that it is a challenge to operate floating drilling rigs and drill ships in a safe manner at all times, when work is carried out above a riser extending from the seabed and up to the vessel, so-called Work Over Riser (WOR) operations. WOR systems dimensioned for steadily increasing pressures combined with that WOR operations are taking place at all times of the year in exposed regions, has increased the likelihood of an uncontrolled situation and damage to equipment in well testing and WOR operations.
In certain situations tension between an equipment in the well and the vessel exceeds the structural strength of the vessel heave compensator, drilling derrick and lifting equipment. Such situations may for example arise at an unexpected high wave and drift-off of the vessel. Modern equipment for well testing may be so heavy that the tension in the drill pipe may exceed the dimensioning maximum load for the vessel lifting equipment. The vessel will stand waves up to the maximum of the heave compensator working range. In certain weather conditions wave heights exceeding the heave compensator working range may occur, and breakage may occur when the heave compensator is maximum outstretched. It is a requirement that such a breakage shall be controlled in such a manner that the breakage occurs in a place it is expected to, thereby avoid damage to personnel and equipment. There is thus a need to introduce a weakened connection giving a controlled breakage to avoid extensive damage.
The riser is arranged to the vessel in such a way that the vessel may move with the waves and such that the riser top moves relative to the vessel work deck. Wireline or coiled tubing is led up and down in the riser by means of a lift. The lift is connected to the heave compensator via a so-called elevator bail, generally via two elevator bails of known type. An elevator bail will typically be provided with an attachment organ in each end portion. The attachment organ may be constituted by an eye arranged to be fastened or unfastened quickly to or from hooks. The elevator bails exist in several lengths and are constituted by solid metal such as a steel alloy.
The lift is hanging in the heave compensator via elevator bails. The lift and the elevator bail are according to prior art connected through a weakened connection, a so-called weak link. Every weak link is split into an upper main part and a lower main part. The lower main part is provided with an attachment organ forming a segmented connection with the lift. The attachment organ may be an eye or a fork fastened to the lift by means of a bolt through the fork prongs. The upper main part is fastened to a lower eye in a pipe handling equipment hanging directly or indirectly in the heave compensator. A fracture bolt arranged to be broken at a predetermined tensile load holds the two main parts together. The weak link is also provided with a hydraulically displaceable bolt constituted by a strong bolt. In lifting the equipment the strong bolt is displaced into complementary openings in the two main parts of the weak link and forms a strong connection between these. When a critical work operation is to be carried out, the strong bolt is pulled out of the complementary openings and the equipment is hanging on the fracture bolt.
The known solution has at least two drawbacks. At a fracture the contact between the two main parts of the weak link is lost and there exists thus no longer a connection between the lift and the heave compensator and appurtenant lifting equipment. The equipment may no longer be lifted up before a connection between the two main parts of the weak link is recreated or that the lift is fastened directly to elevator bails hanging directly or indirectly from the heave compensator. This may not be done before the weather has improved. This also requires personnel to get out on deck, which constitutes a risk. The other drawback is that the connection between the heave compensator and the lift is constituted by an elevator bail and a weak link interconnected through a hook-to-eye connection. This forms a segmented connection being straight when a tension is applied to the lift from below, but which will move out to the side when the vessel movement is downwards and the connection is exposed to compression.
Patent document NO20084595 shows a tension frame for use in well interventions offshore. The tension frame leg is in one of its portions provided with a boring therethrough arranged to accommodate a fracture element. The fracture element may by means of an activator be displaced in its borings along its longitudinal direction between a “strong modus” where the shear forces will act on the full diameter of the fracture element, and a weak modus where the shear forces will act on the weakened portions of the fracture element. The teaching of the patent document does not solve the problem of maintaining and/or recreating the connection between the main parts in the tension frame when the fracture element is broken.
Within the art it is known to use elevator bails that are lengthwise adjustable. The patent document WO 2005/121493 shows an elevator bail comprising a sleeve part provided with an attachment eye and a rod provided with an eye that may be displaced in its longitudinal direction inside the sleeve part. The rod is attached to the sleeve part by bolts through the sleeve part and the rod. The bolts form a fixed connection. Patent document US 2005/0098352 shows an elevator bail having a central sleeve part, an upper rod provided with an attachment eye and a lower rod provided with an attachment eye. The upper rod and the lower rod may be displaced in their longitudinal directions inside the sleeve part. The rods are attached to the sleeve part by means of bolts going through the sleeve part and the respective rod. Both of these patent documents teach about statically longitudinally adjustable elevator bails, meaning that when they are in use they have fixed lengths. Changing of the elevator bail length requires that bolts are taken out of their respective through holes and are put back in after the rod has been displaced inside the sleeve part to its desired length.